The myocardial response to behaviorally conditioned pressor responses will be investigated in intact, unanesthetized baboons to determine the effect of such events upon isolated segments of cardiac muscle during control vs. acute periods of coronary occlusion. The increases in blood pressure will be elicited using a classical appetitive conditioning paradigm. Changes in muscle segment length will be assessed in normally oxygenated, marginally oxygenated and ischemic portions of the myocardium using ultra-sound techniques. Acute periods of myocardial ischemia will be produced by temporarily inflating a pneumatic occluder placed around the left anterior descending coronary artery. The behavioral conditioning trials will be conducted during control periods as well as during 5-minute long occlusions of the coronary vessel. In a corollary experiment, the role of the automatic nervous system in mediating the cardiovascular response to coronary occulusion in intact dog will be assessed. More specifically, the heart rate, blood pressure and cardiac output changes induced by 5-minute occlusions of the left circumflex cornary artery in intact, sedated dog will be determined during control conditions and during trials where blood pressure is not permitted to drop by using Lambson bottles to "clamp" pressure. These experiments combined with data from previous work, will permit us to assess the relative roles of the arterial baroreflexes and the cardio-cardiac reflexes in mediating the acute response to coronary occlusion in dog. Finally, the changes in coronary vascular resistance during classical aversive conditioning will be studied in dogs using ultra-sound flow probes to measure left circumflex flow. Alpha adrenergic blocking agents will be used to assess the involvement of neurally induced vasoconstriction during behavioral stress in dog.